09/30/2016. Remarks by Johan Visschedijk: "In 1938, the nose of the DB-3B was completely redesigned - the cumbersome nose turret being replaced by a slim, glazed pointed nose with a swivel gun-mounting. The back of the pilot's seat was provided with 0.35 in (9 mm) armor protection. Altitude performance was improved by replacing the M-86 with the M-87 A which had the same takeoff power but developed 900 hp at 15,420 ft (4,700 m), and by fitting the new VISh-23 three-blade variable-pitch metal propeller with a diameter of 11 ft 2 in (3.4 m). Oil-cooler intakes were extended forward to the leading edge of the cowling. Armament and bomb load of the latest version which was designated DB-3F (forsirovannie - boosted) was the same as on the DB-3B, except that the rear gunner's ventral weapon was now on a hinged mounting. The DB-3F completed its State trials in June, 1939.
In 1942, the M-87A was replaced by the 1,100 hp M-88B with a two-speed supercharger; with this engine takeoff power was maintained up to 13,120 ft (4,000 m); and at 19,685 ft (6,000 m) the M-88B developed 1,000 hp. At about the same time the rear gunner's ShKAS machinegun was replaced by a single 0.50 in (12.7 mm) DBT heavy caliber machinegun, and the new-style designation Il-4 allocated. During the period in 1942 when wooden wing spars replaced the metal spars while light alloys were in short supply, there was a small increase in gross weight and a 2.5 mph (4 kmh) reduction in speed. The Il-4's navigational equipment included a radio compass and APG-1 autopilot
During the WW II the Il-4 was used in a variety of roles. Not only was it the only Soviet long-range bomber (excluding a handful of Pe-8s) but it was also used tactically, for photographic reconnaissance, glider towing, and even carried seven men and their equipment as a troop transport and was also used by the Navy as a torpedo-bomber (see 3-view) when a 17.72 in (450 mm) 2,072 lb (940 kg) 45-36-AN (low level) or 45-36-AV (high-level) torpedo was carried beneath the fuselage, with a small compressed-air tank behind for running up the torpedo before release.
Between 1937 and 1940, 1,528 DB-3s were produced; modern production methods were introduced in 1940 and between then and 1944 when production ceased, 5,256 DB-3Fs and Il-4s were built. The DB-3F was the first Soviet aircraft to bomb Berlin during the war when a formation of long-range bombers, of the 1st Guards Mine/Torpedo Bomber Aviation Regiment of the VVS Baltic Fleet, under the command of Colonel E. N. Preobrazhenskii, attacked the German capital during the night of August 8, 1941.
Both the DB-3B and DB-3F were used on the Finnish Front, and in 1944, the Finnish PLeLv 46 bomber squadron operated three of each alongside its Dornier bombers."